Very high quality requirements are imposed in particular on coating compositions employed in the area of automotive refinishing. For instance, these coating compositions must be fully curable at low temperatures (&lt;100 degrees C., preferably&lt;80 degrees C.) and in this context should be dust-dry and tack-free even after less than 7 hours. Moreover, good solvent resistance, weathering resistance, masking resistance, yellowing resistance, sandability and a low inherent color of the resulting coatings are required. In addition to this, the coatings must be able to be overpainted in order thus to insure that it is also possible to repair paint damage in the adjacent area.
In the area of the finishing of large-size vehicles, for example the finishing of truck bodies, the masking resistance of the resulting coatings is of particular importance. Large-size vehicles are commonly provided with written characters for whose application it is necessary to mask off the adjacent area. If the masking resistance is inadequate, the marks must be removed manually, by laborious sanding and polishing, which entails a considerable financial outlay.
DE-A-41 24 167 discloses clearcoats for automotive finishing which as binders contain copolymers in which from 9 to 20% by weight of a methoxy-functional polysiloxane has been incorporated by condensation. These clearcoats however, owing to the high proportion of polysiloxane, have the disadvantage that the topcoat holdout or the leveling of the clearcoats is adversely affected.
Furthermore, EP-A-603 561 discloses coating compositions which as binders contain copolymers in which from 3 to 40% by weight of an alpha,omega-hydroxy-, -carboxy- and/or -epoxy-functional polysiloxane has been incorporated by polymerization.
JP-A-2-163177 comprises a coating composition based on hydroxyl-containing acrylate copolymers and polyisocyanates which is employed, in particular, as a masonry coating composition. In this case the coatings are notable for improved weathering stability, which is obtained by copolymerization of from 0.5 to 15% by weight of a polysiloxane macromonomer into the hydroxyl-containing acrylate copolymer. The use of a reaction product of acrylic and/or methacrylic acid with the glycidyl ester of an alpha-branched monocarboxylic acid having 5 to 18 carbon atoms as monomer component, however, is not described in this document.
These coating compositions known from JP-A-2-163177 have, in particular, the disadvantage that the topcoat holdout or leveling of the coating compositions described is adversely affected by the high siloxane content of the copolymers which are employed as binder.
U.S. Pat. No. 4,754,014 discloses coating compositions based on hydroxyl-containing acrylate copolymers which are modified with polysiloxane macromonomers. The polysiloxane macromonomers are prepared by reacting a hydroxy-functional polysiloxane with an epoxy-functional acrylate. These coating compositions known from U.S. Pat. No. 4,754,014 exhibit a high flexibility and are therefore particularly suitable for the coating of plastics materials, for example fenders. These coating compositions differ from the coating compositions of the present application, in particular, in that the use of a reaction product of acrylic and/or methacrylic acid with the glycidyl ester of an alpha-branched monocarboxylic acid having 5 to 18 carbon atoms per molecule as monomer component for preparing the hydroxy- functional acrylate copolymers, and the specific combination of hydroxy-functional acrylate component, polyester-modified polyacrylate and crosslinking component, is not described in this document.
Finally, EP-B-175 092 discloses that the flow properties and the lubricity and mar resistance of coatings can be improved by adding polyester-modified siloxanes which are free from polyether groups to the coating compositions. The use of polymerizable, ethylenically unsaturated polysiloxane macromonomers to modify binders based on acrylate copolymers is not described in EP-B-175 092.
The as yet unpublished U.S. patent application Ser. No. 08/396,028 comprises a coating composition consisting of (A) at least one hydroxyl-containing polyacrylate resin, containing as comonomer units polysiloxane macromonomers (a5) and reaction products of acrylic and/or methacrylic acid with the glycidyl ester of an alpha-branched monocarboxylic acid having 5 to 18 carbon atoms per molecule (a3), of (B) at least one isocyanate crosslinking agent and, if desired, of (C) at least one hydroxyl-containing, polyester-modified polyacrylate resin. The present invention differs from the U.S. patent application Ser. No. 08/396,028 by the presence, in accordance with the invention, of component (C) in specific proportions by weight relative to the binder.
The likewise as yet unpublished German Patent Application 195 19 807.7 describes coating compositions comprising (A) at least one hydroxyl-containing component consisting of (A1) at least one polyester and (A2) at least one hydroxyl-containing polyacrylate resin which has been prepared at least partially in the presence of component (A1), and (B) at least one crosslinking agent. Furthermore, the as yet unpublished German Patent Application 195 19 807.7 also describes the use of such coating compositions in processes for the production of protective and/or decorative coatings on substrate surfaces and the use of the coating compositions in the area of automotive refinishing. The additional use of hydroxyl-containing acrylate copolymers with polysiloxane macromonomers and reaction products of acrylic and/or methacrylic acid with the glycidyl ester of an alpha-branched monocarboxylic acid having 5 to 18 carbon atoms per molecule as comonomer units is not described in P 195 19 807.7.